Down hole physical upgrading of heavy crude oils by selective energy absorption

ABSTRACT

The present invention utilizes the ability of electromagnetic energy at the appropriate frequency to selectively deposit thermal energy in the heavy oil for precise control of cracking temperature throughout a given volume of material. Selective electromagnetic energy absorption in the heavy crude oil provides energy efficient transfer of heat at the molecular level and thereby insures precise temperature control throughout the treatment volume. This allows for optimization of the visbreaking process using electromagnetic energy.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority from U.S. provisional patentapplication No. 60/645,154, which was filed on Jan. 19, 2005, and whichis incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to the use of electromagneticenergy to subject heavy crude oil to mild thermal cracking conditions,thereby lowering the viscosity, pour point, and specific gravity of theoil and rendering it easier to recover and handle. More particularly,this invention relates to methods for applying electromagnetic energy toheavy oils in the reservoir to promote in situ upgrading and facilitaterecovery. This invention also relates to systems to applyelectromagnetic energy to heavy oils in situ.

BACKGROUND OF THE INVENTION

Heavy crude oil presents problems in oil recovery and production. Crudeoils of low API gravity and crude oils having a high pour point presentproduction problems both in and out of the reservoir. Extracting andrefining such oils is difficult and expensive. In particular, it isdifficult to pump heavy crude oil or move it via pipelines.

Various methods to ameliorate the disadvantages of heavy crude oil areused today. For example, the oil industry reduces surface handlingproblems by blending heavy crude oil with light oils and liquid propranegas to make them easily handled in pipelines and storage facilities.This method has drawbacks, however, as it does not assist in the initialrecovery of the oil, and it is expensive.

A process called “visbreaking,” or mild thermal cracking, may also beused to reduce the viscosity of heavy crude oil. “Visbreaking” is an oilrefinery process for increasing the pumpability of heavy crudes. Ittypically is accomplished by heating heavy crude oil in a furnace. Theprocess is characterized by mild decomposition, minimum coke formationand the retention of the cracked product in the original feed stock. Theresultant mixture has viscosity, pour point, and specific gravity valuesthat are lower than the original oil. However, ask applied today,visbreaking cannot be used on oil in situ.

The present invention applies visbreaking new contexts and for newpurposes, and proposes improved methods for the application ofvisbreaking. In the present invention, visbreaking is accomplished usingelectromagnetic energy to heat the heavy crude oil, rather than heatingit in a furnace. Furthermore, the present invention is suitable for usein the treatment of oil in situ. Such treatment permits the upgrade ofthe oil in reservoir and assists in the recovery of the oil.

BRIEF SUMMARY OF THE INVENTION

The present invention utilizes the ability of electromagnetic energy atthe appropriate frequency to selectively deposit thermal energy in theheavy oil for precise control of cracking temperature throughout a givenvolume of material. Selective electromagnetic energy absorption in theheavy crude oil provides energy efficient transfer of heat at themolecular level and thereby insures precise temperature controlthroughout the treatment volume. This allows for optimization of thevisbreaking process using electromagnetic energy.

Proper selection of frequency and power duration results in the rapidcracking of heavy hydrocarbons to any degree desired by electromagneticenergy absorption. When the desired degree of cracking is reached, thehot oil matrix provides a significantly different set of electricalproperties which can be measured on the surface during the“electromagnetic visbreaking process.” (EVP) to insure precise down holetemperature and power control.

This proposed EVP provides efficient energy absorption and control ofthermal cracking of heavy oils for in-situ upgrading. The application oflow power (a few ten's of kilowatts) electromagnetic energy to theformation for visbreaking will provide mild decomposition of the heavyoil, minimum coke formation and the retention of the cracked product inthe original feedstock. The resultant mixture has viscosity, pour point,and specific gravity values which are lower than those of the originaloil.

The present invention several promising applications. It can be used toupgrade heavy crude oil in situ. It can also assist in the recovery ofheavy crude oil from reservoirs. Further, the present invention can beused to more efficiently recovery hydrocarbons from oil shale, such asthat present in the Western United States.

In one embodiment of the invention, a system may be provided for use intreating heavy crude oil underground. The system may comprise a boreholein an area in which crude oil exists in the ground, an electromagneticenergy applicator positioned within the borehole in the vicinity of theheavy crude oil to be treated, a cable attached to the electromagneticenergy applicator to supply electromagnetic energy to the applicator, anelectromagnetic energy generator attached to the cable to generateelectromagnetic energy to be supplied to the applicator, and a productreturn pipe running through the borehole, the product return pipecomprised of a distal end positioned in the vicinity of theelectromagnetic energy applicator through which oil or other productsmay be recovered and a proximal end on or near the surface of theground.

In another embodiment of the invention, a method for treating heavycrude oil underground is provided. The method comprises the steps ofpositioning an electromagnetic energy applicator in a borehole in thevicinity of heavy crude oil, generating electromagnetic energy, applyingthe electromagnetic energy to the heavy crude oil with the applicator toachieve thermal cracking, and recovering heavy crude oil through aproduct return pipe.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. As will be realized, theinvention is capable of modifications in various obvious aspects, allwithout departing from the spirit and scope of the present invention.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a single borehole radiation typeapplicator.

FIG. 2 is a close up view of a portion of the applicator system.

FIG. 3 is a perspective view of a portion of another configuration of asingle borehole applicator.

FIG. 4 is a perspective view of a wellhead for use with the applicatorsystem.

FIG. 5 shows a sample of the absorption data from experiments on theapplication of electromagnetic energy to large oil molecules in oilshale.

DETAILED DESCRIPTION

A variety of different types of down hole electromagnetic structures maybe employed to apply electromagnetic energy to heavy crude oil in situ.The proper structure for any particular application depends on a varietyof factors, including depth, heat uniformity, and minimizing the degreeof coking and production of unsaturated hydrocarbons.

FIG. 1 is a perspective view of a single borehole radiation typeapplicator. Applicator system 10 is positioned within borehole 12.Borehole 12 is supported by casing 14. Applicator system 10 is then usedto apply electromagnetic energy to heavy crude oil in the vicinity ofborehole 12.

Applicator structure 20 is a transmission line retort. For a point ofreference, a typical applicator 20 may be approximately 70 feet long. Ina typical configuration, the applicator 20 may be positioned frombetween 100 to 600 feet underground in borehole 12. Radiofrequency(“RF”) energy is supplied to applicator 20 by an RF generator (notshown). The RF generator is connected to applicator 20 via a portion offlexible coaxial cable 30. In turn, the flexible coaxial cable 30 isconnected to a portion of rigid coaxial cable 32. The coaxial cable mayor may not be supported by ceramic beads, which are desirable at highertemperatures. By this means, the RF generator supplies RF energy toapplicator 20, which in turn applies RF energy to the target volume toachieve visbreaking. This allows in situ upgrading of the heavy crudeoil and assists in recovery.

Recovery of the oil and related products is achieved by means ofproduction pipe 40. This non-metallic pipe runs from the production areaof borehole 12 through the borehole to surface 16. At the surface,production pipe 40 is connected via a product return line to a storageor processing facility (no shown).

Production pipe 40 provides a firm mounting base for the RF hardware ofapplicator system 10. Coaxial cables 30 and 32 can be attached directlyto production pipe 40 using connectors 42. Applicator 20 also attachesto production pipe 40.

FIG. 2 is a close up view of a portion of the applicator system.Applicator structure 20, rigid coaxial cable 32, and production pipe 40are all positioned within borehole 12. Typical dimensions for such asystem are shown in FIG. 2. Ceramic support beads 34 support rigidcoaxial cable 32. Further, ceramic pressure window 36 is placed at thetope of applicator 20.

FIG. 3 is a perspective view of a portion of another configuration of asingle borehole applicator. In this configuration, a dipole feed isused. Coaxial feed 38 surrounds production pipe 40. Ceramic window 36 isplaced at the bottom of coaxial feed 38.

Although specific examples of applicator structures are given, it isunderstood that other arrangements known in the art could be used aswell. Uniform heating may be achieved using antenna array techniques,such as those disclosed in U.S. Pat. No. 5,065,819. Such techniques canbe used to minimize coking conditions at the applicator borehole andavoid excessive electrode voltage gradients at high power. Arrays reduceexcessive voltage gradients at the borehole by means of mutual coupling.The ability to separately measure reflected power from each applicatorborehole containing radiator and mutual impedance coupling between anypair of applicator boreholes insures precise temperature control of theheated volume.

Other variations are possible, including non-radiation structures suchas those proposed in J. Bridges, et al., “RF Heating of Utah Tar Sands,”Final Report, IIT Research Institute. However, such structures aresensitive to high voltage breakdown and require extensive drilling whichis not economical.

A special wellhead may be used in conjunction with applicator system 10.Properly designed, the wellhead can be used to provide safe andefficient delivery of RF energy to the applicator.

FIG. 4 is a perspective view of a wellhead for use with the applicatorsystem. The weight of the down hole applicator (not shown) rests on aspecial bellows 46 within the wellhead. This insures that any heatinduced mechanical movements of the down hole apparatus during energytransfer do not interrupt power flow. An input opening 44 permitsnitrogen to be introduced into the interior of the wellhead andborehole, further ensuring the safe application of RF energy. Insulators45 are positioned above the bellows 46, and a center conductor expansionjoint is positioned on top of that. At the top of the wellhead, wherecoaxial cable 30 exits and runs to RF generator 28, a coaxial line sealand vertical alignment clamp 26 secure the cable to the wellhead.Product return line 41 carries the product recovered through the systemto a storage or processing facility (not shown), and water extractionline 43 permits the removal of water from borehole 12.

The present invention also has application in oil shale fields, such asthose present in the Western United States. Large oil molecules thatexist in such oil shale have been heated in a series of experiments toevaluate the dielectric frequency response with temperature. Theresponse at low temperatures is always dictated by the connate wateruntil this water is removed as a vapor. Following the water vapor state,the minerals control the degree of energy absorption until temperaturesof about 300-350 degrees centigrade are reached. In this temperaturerange, the electromagnetic energy begins to be preferentially absorbedby the heavy oil. The onset of this selective absorption is rapid andrequires power control to insure that excessive temperatures withattendant coking do not occur. FIG. 5 shows a sample of the absorptiondata from such experiments.

Because of the high temperature selective energy absorption capabilityof heavy oil, it is therefore possible to very carefully control thebulk temperature of down hole crude oil heated by electromagneticenergy. The energy requirement is minimized once the connate water isremoved by steaming. It takes much less energy to reach mild crackingtemperatures with electromagnetic energy than any other thermal means toprovide visbreaking.

Kasevich has published a molecular theory that relates to the specificheating of heavy of oil molecules. He found that by comparing cableinsulating oils with kerogen (oil) from oil shale, a statisticaldistribution of relaxation times in the kerogen dielectric gave the besttheoretical description of how electromagnetic energy is absorbed in oilthrough dielectric properties. With higher temperatures and lowering ofpotential energy barriers within the molecular complex a rapid rise inselective energy absorption occurs.

In use, a user of an embodiment of the present invention would positionan applicator system in a borehole in an area in which heavy crude oilexists. The user would position the applicator structure itself in theborehole in the target area for application of RF energy. The user wouldconnect the applicator structure to an RF generator via coaxial cable. Aproduction pipe would run from the area of production to the surface,and from there to a storage or processing facility. The user would thenapply RF energy using the RF generator to the applicator, therebyapplying the RF energy to the heavy crude oil in situ. The RF energywould be controlled to minimize coking and achieve the desired crackingand upgrading of the heavy crude oil. The resulting products would thenbe recovered via the production pipe and transferred to a storage orprocessing facility.

Although the present invention has been described with reference topreferred embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A system for use in treating heavy crude oil underground, the systemcomprising: a borehole in an area in which crude oil exists in theground; an electromagnetic energy applicator positioned within theborehole in the vicinity of the heavy crude oil to be treated; a cableattached to the electromagnetic energy applicator to supplyelectromagnetic energy to the applicator; an electromagnetic energygenerator attached to the cable to generate electromagnetic energy to besupplied to the applicator; and a product return pipe running throughthe borehole, the product return pipe comprised of: a distal endpositioned in the vicinity of the electromagnetic energy applicatorthrough which oil or other products may be recovered; and a proximal endon or near the surface of the ground.
 2. The system of claim 1 whereinthe applicator is an antenna array.
 3. The system of claim 1 wherein theapplicator is a solenoid antenna.
 4. The system of claim 1 wherein theapplicator is a helical antenna.
 5. The system of claim 1 in which atleast one of the cable and applicator are attached to the product returnpipe.
 6. The system of claim 1 in which the product return pipe isconnected to a storage or processing facility.
 7. The system of claim 1further comprising: a wellhead at the surface of the borehole, thewellhead comprising: a bellows connected to the applicator structure insuch a way that the bellows supports the weight of the applicator. 8.The system of claim 7 further comprising a sealable opening for theintroduction of gas to the wellhead and borehole.
 9. A method fortreating heavy crude oil underground, the method comprising the stepsof: positioning an electromagnetic energy applicator in a borehole inthe vicinity of heavy crude oil; generating electromagnetic energy;applying the electromagnetic energy to the heavy crude oil with theapplicator to achieve thermal cracking; and recovering heavy crude oilthrough a product return pipe.
 10. The method of claim 9, furthercomprising the steps of: controlling the electromagnetic energy appliedto the heavy crude oil in order to upgrade the heavy crude oil in situ.11. The method of claim 9, in which the electromagnetic energy isapplied to heavy crude oil in oil shale.